This invention relates to a holder of pipes or pipe joints for welding, which can hold the root opening of the pipes or the pipe joints uniform in the case of butting the end portions of pipes or pipe joints.
Generally, in welding of pipes or pipe joints on the pipe assembly works, there has been used welding means of one side butting from outside. The end portions of pipes or pipe joints to be welded are provided with welding grooves respectively, and the groove angle, root opening, etc. in the welding groove are determined according to pipe thickness and welding methods.
The condition of welding groove gives an important influence to the welding result, so that the pipe ends must be carefully worked so as to be smooth and clean.
Further, it is important that pipe ends are aligned, that dislocation between both pipes is prevented by centering, and that the root opening is kept uniform.
In order to satisfy the above-mentioned important conditions and also hold securely the pipes to be welded, many kinds of external clamps have been employed. However, as these external clamps have complicated mechanisms and are of large size, there existed inconvenience in case of pipe assembly works, such as difficulty in handling. Therefore, as shown in FIG. 1 tack steel plates (c) have been used so that the groove butting condition of the pipes (a) and (b) is held. These tack steel plates are welded at the equal distance in the outer periphery of the pipes, in which the welding operation is made between the pipes (a) and (b) while keeping the root opening (s). The welding of the tack steel plates is made as a preparation work of the pipe assembly works.
Nextly, in the place in which the welding of the tack steel plates finished, the groove portion is welded in the state that the tack steel plates have been welded, and then the tack steel plates are knocked and removed by a hammer, and thereafter the portion of groove which has not yet been welded is welded, and finally the remains of welded metal of the tack steel plate are made flat by a grinder.
The conventional methods as mentioned above cause often such defects that pipes are damaged due to removal of tack steel plates by a hammer and that the remedy of such damage is necessitated by means of a build-up welding and also cracks on the pipes are sometimes found according to the X-ray research.